[FFmpeg-devel] [PATCH] mp4 and ipod metadata

Baptiste Coudurier baptiste.coudurier
Fri Jun 13 08:54:14 CEST 2008

Michael Niedermayer wrote:
> On Thu, Jun 12, 2008 at 08:17:02PM -0700, Baptiste Coudurier wrote:
>>>>>> [....]
>>>>>> So yes, we may set ChannelCount to either 1 or 2 for MPEG-4, in the
>>>>>>  sense that we are not creating "pure" MPEG-4, but I object to set 
>>>>>> it to 6 until ISO clarify, and I really do not understand why they 
>>>>>> do not clarify.
>>>>> I do understand why they do not clarify. There is nothing to clarify.
>>>>>  There is a field which can contain either 2 (the default value) or 
>>>>> the channel count.
>>>> You don't seem to be reading correctly:
>>>> "ChannelCount is either 1 (mono) or 2 (stereo)"
>>> I cannot help you if you do not want to understand the spec.
>> Me neither, if you want to hack specs and make them stating what they do
>> not.
> But you are doing that. The specs state many times that they are compatible
> you claim that channel count would have to be set to different incompatible
> values in 3gp and mj2 or what it was.

We cannot put 'mjp2':

"Files conformant with this specification must contain at least one
Motion JPEG2000 video track. They may contain more video tracks,
uncompressed audio, or compressed MP4 audio."

ChannelCount is ignored by mp4 and 3gp, there is no point setting it to
something else than 2.

>>> [...[
>>> And above all even if no spec defined it, that would not affect that
>>> its default value of 2 would be valid for all specs then (as none
>>> defined it otherwise).
>>> Its kinda simple either one defines it or none defines it. Either way
>>> there the incompatibility you claimed does not exist.
>>> Whats even more ridiculous is that you insist to only support a ancient
>>> revission of the 3gp spec because the later REQUIRE all 3gp files to
>>> claim to be iso media compatible. And you seem to prefer if they are
>>> not compatible.
>> This is false. 
> what is false?

That I insist to only support an ancient revision. I dont prefer them
not being compatible, I'm definitely ok to put 'isom' in compatible
brands, and as much compatible brands that it is possible.

Im not ok with filling useless fields with potentially dangerous values,
like ChannelCount.

>> 3gp4 can be supported by all later releases, being
>> ancient or not. 
>> What I don't not want to is to change major brand, you
> And i didnt ask you to change it, are we just fighting each other over
> nothing? Or is there some actual disagreement left?

Not really.

>> can add more compatible brands if you want like "isom", but not "mp41"
>> nor "mp42", since those files wouldn't be, we miss crappy tracks.
> good, what about adding 3gp* to our mp4s? (i of course would remove them
> again if they cause problems for some players)

I think we can put "isom" and some of the 3gp brands to our mp4, if mp4
contains H.264, it would only be compatible with 3gp6 though.

> Besides, its offtopic but we need to fix our muxer to add these "tracks"
> one day a well. I wonder how hard it is to generate some empty dummy tracks
> to conform to the spec ...

Yeah, I'd love to put "mp42" as major brand to our mp4, what we need is
"iods" atom and hdlr osdm/sdsm bifs tracks.

>>> [...]
>>> They cannot, simply because a .mp4 wont work on a 3gp device and a .3gp
>>> wont work on a .mp4 device. You explicitly claim in the compatible brands
>>> in ftyp that the other one isnt supported.
>> Please tell me how do you put amr in .mp4 ? Playable by Quicktime.
>> Will you test your code against Quicktime ? Phones ?
> I wont test against QT, that iam pretty sure.

Well, many of our users will use/play created files with Quicktime.


Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
Smartjog USA Inc.                                http://www.smartjog.com
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA

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